1. Field of the Invention
The present invention relates to an image forming apparatus, a control method therefor, and a storage medium.
2. Description of the Related Art
In recent years, in terms of improvement of environmental awareness and reduction of an electricity rate, it has been desired to reduce power consumption for general electric appliances. Therefore, image forming apparatuses having a power saving mode (energy saving mode) in which power consumption is lower than that in a normal operation mode are increasing.
It is well known that in an image forming apparatus adopting an electrophotographic method which forms a toner image on a recording material and thermally fixes the formed toner image on the recording material by a fixing device, the power consumption of the fixing device accounts for most of the power consumption of the image forming apparatus. The following technique has thus been proposed. That is, when the image forming apparatus in the energy saving mode has not been used for a given time or longer, the temperature of the fixing device is lowered to reduce power supply to a heating unit (heater) included in the fixing device, thereby reducing the power consumption of the image forming apparatus. For example, Japanese Patent Laid-Open No. 2006-162864 proposes a technique of prompting a user to input power consumption or an electricity rate when an image forming apparatus is in a standby state, and controlling the temperature of a fixing device in the standby state based on the input value.
For the image forming apparatus adopting an electrophotographic method, the temperature of the fixing device is generally set in advance, and a largest amount of a color material (toner) applicable on a recording material is determined based on the set fixing temperature. Since especially a multi-color image forming apparatus performs image formation by superposing toners of a plurality of colors such as C (cyan), M (magenta), Y (yellow), and K (black), the amount of toner applied on the recording material tends to be large. In such multi-color image forming apparatus, a fixing temperature is set to obtain sufficient fixation even if the largest amount of toner is applied on a recording material. Japanese Patent Laid-Open No. 11-125987 proposes control of a fixing operation based on toner consumption amount information, which is applicable to a multi-color image forming apparatus. The image forming apparatus described in Japanese Patent Laid-Open No. 11-125987 lowers the fixing temperature of a fixing device in the power saving mode, and starts a printing operation when it is determined based on a toner consumption amount corresponding to an input image that a fixing operation is possible even if the fixing temperature has not reached a predetermined temperature. With this processing, an attempt is made to reduce the power consumption and shorten a time to return from the energy saving mode. (The amount of toner applied on a recording material will be referred to as an “amount of applied toner” hereinafter).
The above-described conventional technique, however, pays attention to only power consumption in the standby state, and performs no control of power consumption while an image forming (printing) operation is actually executed. When the image forming apparatus executes print processing at a high frequency, it almost never shifts to the standby state (energy saving mode), and thus the above-described conventional technique may not sufficiently reduce the power consumption.
Furthermore, in recent years, to level out power demands, power suppliers have introduced time-zone pricing which sets different electricity unit prices for different time zones. It is, therefore, desirable to attempt to reduce power consumption and electricity rate in an image forming apparatus by controlling the power consumption according to a change in electricity unit price. The above-described conventional technique, however, cannot perform such control.